Zheng Yingkui

Small-signal model parameter extraction for AlGaN/GaN HEMT

A new 22-element small signal equivalent circuit model for the AlGaN/GaN high electron mobility transistor (HEMT) is presented. Compared with the traditional equivalent circuit model, the gate forward and breakdown conductions (G gsf and G gdf) are introduced into the new model to characterize the gate leakage current. Additionally, for the new gate-connected field plate and the source-connected field plate of the device, an improved method for extracting the parasitic capacitances is proposed, which can be applied to the small-signal extraction for an asymmetric device. To verify the model, S-parameters are obtained from the modeling and measurements. The good agreement between the measured and the simulated results indicate that this model is accurate, stable and comparatively clear in physical significance.

Annealing before gate metal deposition related noise performance in AlGaN/GaN HEMTs

For a further improvement of the noise performance in AlGaN/GaN HEMTs, reducing the relatively high gate leakage current is a key issue. In this paper, an experiment was carried out to demonstrate that one method during the device fabrication process can lower the noise. Two samples were treated differently after gate recess etching: one sample was annealed before metal deposition and the other sample was left as it is. From a comparison of their Ig–Vg characteristics, a conclusion could be drawn that the annealing can effectively reduce the gate leakage current. The etching plasma-induced damage removal or reduction after annealing is considered to be the main factor responsible for it. Evidence is given to prove that annealing can increase the Schottky barrier height. A noise model was used to verify that the annealing of the gate recess before the metal deposition is really effective to improve the noise performance of AlGaN/GaN HEMTs.

AlGaN/GaN high electron mobility transistor with Al2O3+BCB passivation

In this paper, A12O3 ultrathin film used as the surface passivation layer for Al Ga N/Ga N high electron mobility transistor(HEMT) is deposited by thermal atomic layer deposition(ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition(PECVD) Si N passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency(RF) performance are achieved after applying Al2O3+BCB passivation.For the Al2O3+BCB passivated device with a 0.7 μm gate, the value of f max reaches up to 100 GHz, but it decreases to 40 GHz for Si N HEMT. The f max/ f t ratio(≥ 4) is also improved after Al2O3+BCB passivation. The capacitance–voltage(C–V) measurement demonstrates that Al2O3+BCB HEMT shows quite less density of trap states(on the order of magnitude of 1010cm-2) than that obtained at commonly studied Si N HEMT.In this paper, A12O3 ultrathin film used as the surface passivation layer for AlGaN/GaN high electron mobility transistor (HEMT) is deposited by thermal atomic layer deposition (ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition (PECVD) SiN passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency (RF) performance are achieved after applying Al2O3+BCB passivation. For the Al2O3+BCB passivated device with a 0.7 μm gate, the value of fmax reaches up to 100 GHz, but it decreases to 40 GHz for SiN HEMT. The fmax/ft ratio (≥ 4) is also improved after Al2O3+BCB passivation. The capacitance–voltage (C–V) measurement demonstrates that Al2O3+BCB HEMT shows quite less density of trap states (on the order of magnitude of 1010 cm−2) than that obtained at commonly studied SiN HEMT.

A flat gain GaN MMIC power amplifier for X band application

A flat gain two-stage MMIC power amplifier with a 2.8 GHz bandwidth is successfully developed for X band frequency application based on a fully integrated micro-strip AlGaN/GaN HEMT technology on a semi-insulating SiC substrate. Designed with a binary-cluster matching structure integrated with RC networks and LRC networks, the developed power MMIC gets a very flat small signal gain of 15 dB with a gain ripple of 0.35 dB over 9.1-11.9 GHz at the drain bias of 20 V. These RC networks are very easy to improve the stability of used GaN HEMTs with tolerance to the MMIC technology. Inside the frequency range of 9-11.2 GHz where the measurement system calibrated, the amplifier delivers a pulsed output power of 39 dBm and an associated power added efficiency of about 20% at 28 V without saturation, as the available RF power is limited.

Load-pull measurement analysis of AlGaN/GaN HEMT taking into account number of gate fingers

This paper investigates load-pull measurement of AlGaN/GaN high electron mobility transistors (HEMTs) at different numbers of gate fingers. Scalable small-signal models are extracted to analyze the relationship between each models parameters and the number of devices gate fingers. The simulated S-parameters from the small-signal models are compared with the reflection coefficients measured from the load-pull measurement system at X-band frequencies of 8.8 and 10.4 GHz. The dependency between the number of devices gate fingers and load-pull characterization is presented.

Thermal analysis of AlGaN/GaN High-Electron-Mobility Transistors by Infrared Microscopy

The channel temperature of AlGaN/GaN High-Electron-Mobility Transistor was measured by Infrared Microscopy. The behaviors of the channel temperature distribution, the peak channel temperature and the thermal resistance under DC bias were investigated. IR Microscopy facilitates the study of how the device parameters affect reliability.

A revised approach to Schottky parameter extraction for GaN HEMT

We carry out a thermal storage research on GaN HEMT at 350 °C for 48 h, and a recess phenomenon is observed in the low voltage section of Schottky forward characteristics. The decrease of 2DEG density will be responsible for the recess phenomenon. Because the conventional method is not suitable for this kind of curve, a revised approach is presented by analyzing the back-to-back Schottky junction energy band to extract Schottky parameters, which leads to a consistent fit effect.

Impact of UV/ozone surface treatment on AlGaN/GaN HEMTs

Surface treatment plays an important role in the process of making high performance AlGaN/GaN HEMTs. A clean surface is critical for enhancing device performance and long-term reliability. By experimenting with different surface treatment methods, we find that using UV/ozone treatment significantly influences the electrical properties of Ohmic contacts and Schottky contacts. According to these experimental phenomena and X-ray photoelectron spectroscopy surface analysis results, the effect of the UV/ozone treatment and the reason that it influences the Ohmic/Schottky contact characteristics of AlGaN/GaN HEMTs is investigated.